Power supply system capable of reducing power consumption during interruption of an external input signal given to an operating circuit

ABSTRACT

In a system for use in combination with a power source circuit, a holding circuit is operable in response to interruption of an input signal to deenergize the power source circuit and is put into a self-holding state to hold a stop mode of the power source circuit. The self-holding state is released on arrival of the input signal to unlock the stop mode.

BACKGROUND OF THE INVENTION

This invention relates to a power supply system including an operatingcircuit which is for operating a CRT display unit, a printer unit, andthe like and which is turned on and off in response to supply andinterruption of electric power and, in particular, to a power controlcircuit for controlling the electric power supplied to the operatingcircuit.

Generally, a power supply system of the type described is used tooperate peripheral units of an information processing device such as acomputer. Among such peripheral units, a CRT display unit, a printerunit, or the like is put into operation in response to an input signal,such as a synchronization signal, a video signal, and a control signal,which is supplied from an external apparatus. When a peripheral unit ofthe above-mentioned type is used, it is preferable in view of areduction of power consumption to turn off a power source circuit forthe peripheral unit in absence of the input signal and to turn on thepower source circuit only in the presence of the input signal.

To this end, the power supply system generally includes not only aninput signal source and an operating circuit such as the power sourcecircuit for the peripheral unit but also a power control circuit forturning on and off the operating circuit in response to presence andabsence of the input signal.

Such a conventional power control circuit for carrying out theabove-mentioned operation comprises a detecting circuit for detectingnon-reception of the input signal, and a switching circuit for turningthe operating circuit into a stop mode, namely, an off state when thedetecting circuit detects non-reception of the input signal. When theinput signal is received again, the operating circuit must be recovered.Therefore, the power control circuit is required to additionallycomprise a reception detecting circuit for detecting reception of theinput signal and an auxiliary power source circuit for supplyingelectric power to the reception detecting circuit.

In case where the above-mentioned power control circuit is used, thereception detecting circuit must be kept in an active mode by theauxiliary power source circuit even if the input signal is not received.This results in a complicated circuit structure and an increase of powerconsumption.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a power supplysystem which is capable of reducing power consumption duringinterruption of an input signal given to an operating circuit.

It is another object of this invention to provide a power supply systemwhich is capable of quickly recovering an operating circuit into an onstate when an input signal is received again.

It is still another object of this invention to provide a power supplysystem which has a simplified circuit structure.

It is a further object of this invention to provide a power supplysystem which requires substantially no auxiliary power source circuit.

It is a still further object of this invention to provide a powercontrol circuit which is suitable for the power supply system mentionedabove.

According to this invention, there is provided a power control circuitconnected between a signal source for producing an input signal and anoperating circuit for carrying out a predetermined operation, to put theoperating circuit into an active state in response to arrival of theinput signal and into an inactive state in response to interruption ofthe input signal, the power control circuit comprising a detectingcircuit for detecting the arrival and the interruption of the inputsignal, and a holding circuit which puts the operating circuit into theactive state on the arrival of the input signal and which is kept in aself-holding state during the interruption of the input signal to putthe operating Ocircuit into the inactive state.

According to this invention, there is also provided a power supplysystem comprising a signal source for producing an input signal, a powercontrol circuit connected to the signal source, and an operating circuitconnected to the power control circuit, the power control circuitcomprising a detecting circuit for detecting arrival and interruption ofthe input signal, and a holding circuit which puts the operating circuitinto an active state on the arrival of the input signal and which iskept in a self-holding state during the interruption of the input signalto put the operating circuit into an inactive state.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of a power supply system according to a firstembodiment of this invention;

FIG. 2 is a waveform chart for describing the operation of a powercontrol circuit illustrated in FIG. 1;

FIG. 3 is a waveform chart for describing another operation of the powercontrol circuit illustrated in FIG. 1;

FIG. 4 is a block diagram of a power supply system according to a secondembodiment of this invention;

FIG. 5 is a block diagram of a power supply system according to a thirdembodiment of this invention;

FIG. 6 is a block diagram of a part of a power supply system accordingto a fourth embodiment of this invention;

FIG. 7 is a block diagram of a power supply system according to a fifthembodiment of this invention; and

FIG. 8 is a block diagram of a drive circuit for driving the powersupply system illustrated in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Description will now be made as regards several preferred embodiments ofthis invention with reference to the annexed drawing.

Referring to FIG. 1, a power supply system according to a firstembodiment of this invention comprises a power control circuit 10coupled to a source control circuit 11. The operation of the sourcecontrol circuit 11 illustrated in the figure is controlled by the powercontrol circuit 10. The source control circuit 11 is connected to aperipheral unit (not shown in FIG. 1) such as a CRT display unit of acomputer to supply a power source to the unit.

The source control circuit 11 comprises an a.c. power source 111, arectifying circuit 112, a smoothing circuit 113, and a switchingtransformer 114. The switching transformer 114 has a primary sideconnected to an internal control circuit 115 and a secondary sideconnected to an output circuit 116. A CRT display unit (not shown)externally connected is turned on and off through the output circuit116. The smoothing circuit 113 comprises a condenser C1. The outputcircuit 116 comprises a diode D5 and a condenser C3.

It is assumed here that, in absence of a synchronization signal producedby the computer, the illustrated source control circuit 11 is suppliedwith an electric current (hereinafter referred to as a first current) I1from a synchronization signal discriminating circuit (not shown in thefigure). On the other hand, when the synchronization signal is producedagain by the computer, a second current I2 is caused to flow from anexternal circuit in a manner to be described later. At any rate, thesecond current I2 is given in the form of a pulse current which isshorter than the first current I1.

On the other hand, the power control circuit 10 comprises first andsecond photocouplers 101 and 102 composed of light emitting portionsPCT1 and PCT2 and light receiving portions PCR1 and PCR2, respectively.The light emitting portion PCT1 of the first photocoupler 101 issupplied with the first current I1. On the other hand, the lightemitting portion PCT2 of the second photocoupler 102 is supplied withthe second current I2. The power control circuit 10 comprises an offsignal transmitting circuit 103 for transmitting a signal to bring theinternal control circuit 115 of the source control circuit 11 into anoff state, an off state holding circuit 104 for bringing the internalcontrol circuit 115 into an off state and holding the off state, and areset circuit 105 for transmitting a signal to bring the internalcontrol circuit into an on state and resetting the off state holdingcircuit 104.

The off signal transmitting circuit 103 includes the light receivingportion PCR1 of the first photocoupler 101. The light receiving portionPCR1 has a collector connected through a resistor R3 to a sourceterminal (depicted at Vcc) of the internal control circuit 115. As aresult, the off signal transmitting circuit 103 is supplied with asource voltage Vcc, like the internal control circuit 115.

Although the off state holding circuit 104 is practically formed by athyristor, it is equivalently represented herein by an NPN transistor Q1and a PNP transistor Q2. As illustrated in the figure, an emitter of thePNP transistor Q2 is supplied with the source voltage Vcc while acollector and a base thereof are connected to a base and a collector ofthe NPN transistor Q1, respectively. The base of the NPN transistor Q1is connected to an emitter of the light receiving portion PCR1 of thefirst photocoupler 101.

The reset circuit 105 comprises a resistor R4 connected in cascade to aserial circuit composed of a resistor R1 and the light receiving portionPCR2 of the second photocoupler 102, an NPN transistor Q3 having a baseconnected to a common connection point between an emitter of the lightreceiving portion PCR2 and the resistor R4, and a Zener diode ZD1 havingone end connected to the condenser C1. A collector of the NPN transistorQ3 is connected to the base of the NPN transistor Q1 of the off stateholding circuit 104.

With reference to FIG. 1, description will now be made as regards theoperation of the power control circuit 10 and the source control circuit11 having the above-mentioned structure.

In a normal mode, the source control circuit 11 rectifies an a.c.voltage of the a.c. power source 111 and converts the a.c. voltage intoa d.c. voltage under control of the internal control circuit 115 tosupply the d.c. voltage to the peripheral unit of the computer. In thisnormal mode, it is assumed that the delivery of the synchronizationsignal from the computer is stopped. In this event, the first current I1flows to the light emitting portion PCT1 of the first photocoupler 101.As a consequence, the light receiving portion PCR1 of the firstphotocoupler 101 is turned on and causes an electric current to flowthrough the resistors R2 and R3. Accordingly, the electric current isalso caused to flow to the base of the transistor Q1 of the off stateholding circuit 104. Thus, the transistors Q1 and Q2 become conductiveso that the source voltage Vcc of the internal control circuit 115 has alow level. As a consequence, the source control circuit 11 stops itsoperation and is therefore turned off. This state may be called an offmode. The off mode is maintained by a holding current flowing to thetransistors Q1 and Q2 via the resistor R2.

Referring to FIG. 2 in addition, a relationship between the firstcurrent I1 and the mode of operation of the source control circuit 11 isillustrated. The first current I1 is kept at a high level during atransition period from the normal mode to the off mode. The transitionperiod is depicted by T1.

Referring to FIGS. 1 and 3, description will be made as regards theoperation which is carried out on transition from the off mode to thenormal mode. In this case, the above-mentioned synchronization signaldiscriminating circuit is put into an inactive state even if thesynchronization signal arrives from the computer. In response to thearrival of the synchronization signal, the instantaneous second currentI2 illustrated in FIG. 3 flows from an external circuit, which may be,for example, a circuit exemplified in any one of FIGS. 4, 5, and 6, tothe light emitting portion PCT2 of the second photocoupler 102 for atime period T2 shorter than the time period during which the firstcurrent I1 flows. As a consequence, the light emitting portion PCT2emits light to turn the light receiving portion PCR2 into an on state.As a result, an electric current is caused to flow to a base of the NPNtransistor Q3 through the resistor R1 and the light receiving portionPCR2 to bring the NPN transistor Q3 into a conductive state. When thetransistor Q3 becomes conductive, the transistors Q1 and Q2 are turnedinto an interrupted state to release the self-holding state which hasbeen maintained by the transistors Q1 and Q2.

By the interruption of the transistors Q1 and Q2, the source voltage Vccof the internal control circuit 115 is kept at a high level so that theinternal control circuit 115 starts its operation. The source controlcircuit 11 is turned into an active state and is kept in a normal mode.

Thus, in the illustrated power supply system, the off state holdingcircuit 104 is put into a self-holding state during the off mode. Theself-holding state is released by the external circuit such as thecircuit illustrated in any one of FIGS. 4, 5, and 6. It is thereforepossible to remarkably reduce power consumption during the off mode.

FIG. 4 shows a power supply system according to a second embodiment ofthis invention is specified by a power control circuit 10a shown in FIG.4. More specifically, the illustrated power control circuit 10a servesto supply the electric current to the light emitting portions of thephotocouplers 101 and 102 in FIG. 1. In addition, the power supplysystem is used in combination with a CRT display unit of a computerwhich produces a horizontal synchronization signal and a verticalsynchronization signal. To this end, a synchronization discriminatingcircuit 20 is included in the power supply system to detect the presenceor absence of the horizontal and the vertical synchronization signalshaving an output terminal A connected to an anode of the light emittingportion of the photocoupler 101. The power control circuit 10a comprisesdiodes D1 and D2, a condenser Ca, and the light emitting portion of thephotocoupler 102.

In the normal mode, the synchronization discriminating circuit 20 issupplied with the horizontal synchronization signal and the verticalsynchronization signal from the computer. The synchronizationdiscriminating circuit detects an absence of the horizontalsynchronization signal and/or the vertical synchronization signal andgenerates an electric voltage at the output terminal A. When the outputterminal A is supplied with the electric voltage, the electric currentI1 illustrated in FIG. 2 flows to the light emitting portion of thephotocoupler 101. As a result, power source supply to the CRT displayunit is interrupted.

On the other hand, when the horizontal and the vertical synchronizationsignals are produced again from the computer, the horizontal and thevertical synchronization signals are supplied through the diodes D1 andD2 to the condenser Ca to charge the condenser Ca. When the condenser Cais charged to a voltage level greater than that between a cathode and ananode of the light emitting portion of the photocoupler 102, the currentI2 illustrated in FIG. 3 flows to the light emitting portion of thephotocoupler 102. As a consequence, the light receiving portion of thephotocoupler 102 is turned into a conductive state to restart powersource supply to the CRT display unit.

In the illustrated embodiment, description has been made as regards thecase where presence or absence of the horizontal and the verticalsynchronization signals is discriminated by the synchronizationdiscriminating circuit 20.

Alternatively, presence or absence of either one of the horizontal andthe vertical synchronization signals is selectively discriminated andthe power control circuit 10a may be re-energized by the selectedsynchronization signal.

Referring to FIG. 5, a power supply system according to a thirdembodiment of this invention comprises a synchronization discriminatingcircuit 20 like in FIG. 4 and a power control circuit 10b. In theillustrated example also, the photocouplers 101 and 102 can be used inthose of FIG. 1 and the power supply system of FIG. 5 can be thereforecombined with the circuits 10 and 11 shown in FIG. 1. The power controlcircuit lob has a structure different from that illustrated in FIG. 4and is adapted to the case where the input signal of a pulse shape isinterrupted with a maintained high level. In FIG. 5, when the horizontaland the vertical synchronization signals are no longer received, theelectric voltage is produced at the output terminal A of thesynchronization discriminating circuit 20. The electric current I1illustrated in FIG. 2 flows to the light emitting portion of thephotocoupler 101 and power source supply to the CRT display unit isinterrupted.

The illustrated power control circuit 10b comprises two diodes Da andDb, condensers Cb and Cc, and transistors Qa, Qb, and Qc. When thehorizontal and the vertical synchronization signals are supplied again,the photocoupler 102 is brought into a conductive state.

More specifically, the horizontal and the vertical synchronizationsignals are supplied through the diodes Da and Db to the condenser Cb tocharge the same. On the other hand, the horizontal synchronizationsignal is directly supplied to the condenser Cc also. As a consequence,the transistor Qa and the transistor Qb become conductive at a trailingedge of the horizontal synchronization signal and this conductive stateis maintained. Simultaneously, the electric current from the transistorQa is supplied also to the photocoupler 102 to bring the light receivingportion of the photocoupler 102 into a conductive state to provide theelectric current I2 illustrated in FIG. 3.

As a consequence, power source supply to the CRT display unit isrestarted. A source voltage Vcc1 is supplied from a power source circuitof the CRT display unit. Following restart of power source supply, thetransistor Qc becomes conductive. The resultant transistors Qa and Qbare put into an off state to be recovered to an original state. Thus,the circuit illustrated in FIG. 5 can perform the operation similar tothe other embodiments.

Referring to FIG. 6, a power supply system according to a fourthembodiment of this invention is specified by a power control circuit 10cwhich serves to drive the photocoupler 102 illustrated in FIG. 1. Thepower control circuit 10c is adapted to the case where the input signal,such as the horizontal synchronization signal and the verticalsynchronization signal, is a pulse signal interrupted at a high leveland has a low peak-to-peak value. The remaining portion of the powercontrol circuit 10c except the illustrated portion is similar to thoseof FIGS. 4 and 5 and therefore omitted from FIG. 6 for simplicity ofillustration.

The power control circuit illustrated in FIG. 6 comprises condensers C1,C2, and C3, diodes D1, D2, and D3, two transistors QA and QB operable asa thyristor, a resistor, and a transistor QC. The output side of thepower control circuit is connected to the light emitting portion of thephotocoupler 102. The light receiving portion and the remaining portionfollowing the light receiving portion are similar in structure to thoseillustrated in FIG. 1.

In the circuit structure illustrated in the figure, the input signal issupplied to the condenser C3 through the diode D1 and is rectified tokeep a peak value. On the other hand, the input signal passes throughthe condenser C1 and is supplied through the diode D3 to the condenserC2 having one end connected to the condenser C3 to be subjected to peakrectification by the condenser C2. In the illustrated circuit, the diodeD2 is connected to a common connection point between the condenser C1and the diode D3. The input signal passing through the condenser C1 isclamped by the diode D2 with reference to a plus side of the condenserC3. Accordingly, a potential at the other end (depicted at P1) of thecondenser C2 is approximately twice as large as a peak value of theinput signal. When the condenser C2 is charged and the voltage of thecondenser C2 becomes higher than a level sufficient to render thetransistor QA conductive, the transistor QA is put into a conductivestate and a self-holding state is kept by the transistor QB. At thistime, the electric charge stored in the condensers C2 and C3 isdelivered to the photocoupler 102 to flow the electric current I2illustrated in FIG. 3. Thus, power source supply to the CRT display unitis restarted.

Referring to FIG. 7, a power supply system according to a fifthembodiment of this invention comprises a power source control circuit 11similar to that in FIG. 1, and a power control circuit 10d composed ofthe off signal transmitting circuit 103 and the reset circuit 105 bothof which are slightly different in structure from those illustrated inFIG. 1 and the off state holding circuit 104 similar in structure tothat in FIG. 1.

In this embodiment, the operation similar to FIG. 1 can be carried outby the use of the single photocoupler 101. For this purpose, theillustrated system comprises a common circuit 106 for using the lightreceiving portion PCR1 corresponding to the light emitting portion PCT1of the photocoupler 101 in common by the off signal transmitting circuit103 and the reset circuit 105. As illustrated in the figure, the commoncircuit 106 comprises the resistor R1 connected to the collector of thelight receiving portion PCR1. The collector is connected to the Zenerdiode ZD1 having one end connected to the condenser C1.

The emitter of the light receiving portion PCR1 is connected to the offsignal transmitting circuit 103 and the reset circuit 105.

The illustrated reset circuit 105 comprises the NPN transistor Q3. Thebase of the transistor Q3 is connected to the light receiving portionPCR1 through the resistor R4 and a Zener diode ZD3. The emitter and thecollector are connected to the condenser C1 and the base of thetransistor Q1, respectively. On the other hand, the off signaltransmitting circuit 103 comprises an NPN transistor Q4 and a PNPtransistor Q5. The transistor Q4 has a base connected to a Zener diodeZD2. The condenser C2 is connected between a cathode of the Zener diodeZD2 and an emitter of the transistor Q4. The emitter of the transistorQ4 is also connected to the condenser C1. A collector of the transistorQ4 is connected through the diode D3 to a common connection pointbetween the Zener diode ZD3 and the resistor R4 of the reset circuit 105and is connected through a diode D4 to the base of the transistor QS.

A common connection point between the Zener diode ZD2 and the condenserC2 is connected through a resistor R5 and the diode D2 to the emitter ofthe light receiving portion PCR1 on one hand and is connected throughthe diode D1 to the resistor R2 on the other hand.

Description will be made about the operation of the power controlcircuit 10d and the source control circuit 11 both of which areillustrated in FIG. 7 and which may be used in combination with acircuit which is illustrated in FIG. 8 and which drives the photocoupler101, as will become clear.

In the normal mode, the power control circuit 10d is inactive becausethe electric current I1 does not flow to the light emitting portion PCT1of the photocoupler 101. In this state, when the synchronization signalproduced from the computer is assumed to be stopped, the electriccurrent I1 shown in FIG. 2 flows to the light emitting portion PCT1 ofthe photocoupler 101. The electric current flows to the light receivingportion PCR1 through the resistor R1. As a consequence, the electriccurrent flows through the resistor R4 to the base of the transistor Q3to bring the transistor Q3 into a conductive state.

Simultaneously, the electric current flows to the condenser C2 throughthe diode D2 and the resistor R5. When a voltage across the condenser C2exceeds a sum of a Zener voltage of the Zener diode ZD2 and abase-emitter voltage of the transistor Q4, the transistor Q4 is alsoturned into a conductive state. When the transistor Q4 becomesconductive, the transistor Q3 connected through the diode D3 to thetransistor Q4 is turned into an interrupted state. On the other hand,the transistor Q4 connected through the diode D4 is put into aconductive state. When the transistors Q4 and Q5 are turned into aconductive state as described above, the electric current flows to thebase of the transistor Q1 through the resistors R2 and R3 and thetransistor Q5 to bring the transistors Q1 and Q2 into a conductivestate. As a consequence, the source voltage Vcc of the internal controlcircuit 115 has a low level to put the source control circuit 11 into astop mode, namely, an off mode. This off mode is maintained by theelectric current flowing through the resistor R2 to the transistors Q1and Q2.

On the other hand, when the synchronization signal is produced from thecomputer, the circuit illustrated in FIG. 8 produces the short pulsecurrent I2 flowing to the light emitting portion PCT1 of thephotocoupler 101 as illustrated in FIG. 3. The electric cur rent flowsthrough the resistor R1 to the light receiving portion PCR1 of thephotocoupler 101. As a consequence, the electric current flows to thebase of the transistor Q3 through the resistor R4 and the Zener diodeZD3. The transistor Q3 becomes conductive while the transistors Q1 andQ2 are turned into an interrupted state.

At this time, the transistors Q1 and Q2 are not turned into a conductivestate because the transistor Q4 does not become conductive by a pulsecurrent which lasts for a period shorter than a time constant of a timeconstant circuit composed of the resistor R5, the condenser C2, and theZener diode ZD2. As a consequence, the source voltage Vcc of theinternal control circuit 115 has a high level and the source controlcircuit 11 starts its operation to be turned into a normal mode.

Referring to FIG. 8, a drive circuit for driving the power supply systemis connected to the light emitting portion of the photocoupler 101 inFIG. 7 and is operable to cause a current I1 to flow through the lightemitting portion of the photocoupler 101. The illustrated circuitcomprises the synchronization detecting circuit 20 having a functionsimilar to those illustrated in FIGS. 4, 5, and 6, a power controlcircuit 10e, the diodes D1 and D2, the transistor Q1, and the lightemitting portion of the photocoupler 101. The source voltage Vcc1 issupplied from the power source of the CRT display unit.

When no synchronization signal is produced from the computer, the outputterminal A of the synchronization discriminating circuit 20 has a highlevel. The electric current I2 shown in FIG. 2 is given through thediode D1 to the light emitting portion of the photocoupler 101 tointerrupt power source supply to the CRT display unit.

When the synchronization signal is supplied again, the electric currentI2 illustrated in FIG. 3 is given from an output terminal B of the powercontrol circuit 10e through the diode D2 to restart power source supplyto the CRT display unit. Herein, a transistor Q10 is a circuit forpreventing an operation error such as interruption of power sourcesupply in the normal mode.

According to this invention, the power control circuit comprises theholding circuit which is kept in a self-holding state duringinterruption of the input signal to be put in a standby state for theinput signal and which is released from the self-holding state when theinput signal is received again. It is therefore possible to reduce powerconsumption during the standby state for the input signal.

As described above, according to this invention, power consumption ofthe power source circuit for the peripheral unit of the computer duringthe off mode is no more than the electric power required to keep theself-holding state of the transistors. It is noted here that, in priorart, the electric power on the order of 8 watts is essential even in theoff state of the power source circuit. In this invention, the electricpower is reduced down to 5 watts or so. In the foregoing embodiments,the description has been made as regards the source control circuit forcontrolling the power source circuit of the CRT display unit. However,this invention is also applicable to the source control circuit forcontrolling the power source circuit of a printer unit or any other unitwhich is put into operation in response to the input signal.

What is claimed is:
 1. A power control circuit connected between asignal source for producing an input signal and an operating circuit forcarrying out a predetermined operation to put said operating circuitinto a active state in response to arrival of said input signal and inan inactive state in response to interruption of said input signal, saidpower control circuit comprising:a detecting circuit for detecting thearrival and the interruption of said input signal; and a holding circuitwhich puts said operating circuit into the active state on the arrivalof said input signal and which maintains itself in a self-holding stateduring the interruption of said input signal while putting saidoperating circuit into the inactive state, wherein said detectingcircuit comprises: an isolation element which is put into an on state inresponse to the arrival of said input signal; said holding circuitcomprising: a thyristor circuit which is brought into said self-holdingstate in the on state of said isolation element.
 2. A power controlcircuit as claimed in claim 1 wherein said isolation element is aphotocoupler.